Officials at the Environmental Protection Agency are considering whether to bar BP from receiving government contracts, a move that would ultimately cost the company billions in revenue and could end its drilling in federally controlled oil fields. Over the past 10 years, BP has paid tens of millions of dollars in fines and been implicated in four separate instances of criminal misconduct that could have prompted this far more serious action. Until now, the company’s executives and their lawyers have fended off such a penalty by promising that BP would change its ways. That strategy may no longer work.